This invention pertains generally to field emitter flat panel displays and particularly to a method for improving the emission properties of field emitter materials.
Field emitter materials are useful whenever a source of electrons is needed, in particular, for applications such as vacuum microelectronics, electron microscopy and flat panel displays. Flat panel displays which use field emission (cold cathode emission) have several potential advantages over other types of flat panel displays, including low power consumption, high intensity, low projected cost, low turn-on voltage, high site density (&gt;100/pixel) as well as being more stable and robust. For these reasons, field emission displays have the potential to be a low cost, high performance alternative to cathode ray and liquid crystal display technologies. As discussed in W. Zhu et al., Electron Field Emission from Ion-implanted Diamond, Appl. Phys. Lett., 67(8), 21 Aug. 1995, one of the key issues in producing commercially viable field emitters is the development of reliable and efficient field emitter (cold cathode) materials for these devices. At the present time, field emitter materials typically require either complicated fabrication steps or high control voltages to promote emission or both. Furthermore, field emitter materials have several limitations which restrict their usefulness. One limitation concerns the energy imparted to the electrons after they are emitted. Another limitation concerns the uniformity of emission current over the surface of the field emitter material.
The energy which the electric field imparts to electrons after emission can reach a level such that gases surrounding the electron emitter are ionized by the high energy electrons. These ionized gases can, in turn, damage the field emission surface and thereby impair further emission. To reduce the magnitude of the electric field required for electron emission, low work function materials can be used (i.e., special materials that emit electrons at relatively low energy levels) or the emitting surface of the material can be shaped such that the field is concentrated into a small region.
The shape of a field emitter material can affect its emission characteristics. Field emission is most easily obtained from electrically conducting sharply pointed needles or tips. The basic technology useful for fabricating field-imaging structures having this feature has been described by Spindt in U.S. Pat. Nos. 3,812,559, 3,665,241, 3,755,704, 3,789,471 and 5,064,396. Fabrication of these electrically conducting sharply pointed needles or tips requires extensive and elaborate processing steps as well as expensive facilities. It is difficult to perform fine feature lithography on the large areas demanded by flat panel display type applications. Thus there is a need for a method of making flat panel displays using field emitter materials that does not require the complicated and expensive fabrication steps employed to produce the specialized field enhancing shapes (sharply pointed needles or tips) characteristic of "Spindt arrays".
Zhu et al. ibid. have recently shown that diamond possesses properties that make it a desirable material for field emitters. However, little is known about the mechanisms responsible for electron emission from undoped or p-type doped diamond, except that there appears to be a strong correlation between defect densities and emission properties. Geis et al. Diamond Cold Cathode, IEEE Electron Device Letters, 12, 456-459 (1991) report the fabrication and characterization of carbon-implanted diamond materials having current densitites .apprxeq.0.1 to 1 A/cm.sup.2 which compares favorably with silicon cold cathodes. Xu et al. Similarities in the "Cold" Electron Emission Characteristics of Diamond Coated Molybdenum Electrodes and Polished Bulk Graphite Surfaces, J. Phys. D: Applied Phys. 26, 1776-1780 (1993) have shown that substantial electron emission can be obtained at fields as low as 5 V/.mu.m for a graphite-rich diamond film and a diamond-rich graphite electrode. However, while the turn-on voltage (i.e., the minimum voltage required to cause electron emission) for these diamond materials is low, the electron emission is not uniform over the surface but instead appears to arise from isolated sites on the surface of the graphite-rich diamond film. What is needed is an electron emitting material that has a low turn-on voltage wherein the electron emission is uniform across the emitter material surface and wherein the density of electron emission sites is increased.
Responsive to these needs, the present invention provides a method for creating a electron emitter material having a high uniformity of electron emission, a high density of electron emission sites and a low turn-on voltage.